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NOAA: Asian pollution contributes up to 20 percent of West Coast ozone

Plumes waft over Pacific Ocean

By Breanna Draxler For the Camera

Posted:
03/10/2012 11:00:20 AM MST

Updated:
03/10/2012 11:00:25 AM MST

April showers bring May flowers, but April winds bring Asian pollution.

Pollution plumes from East Asia travel over the Pacific Ocean to the western United States and can boost springtime surface ozone levels by 20 percent, according to a new study by the National Oceanic and Atmospheric Administration.

Scientists have long known that pollution wafts over from Asia, but until now they didn't understand how it descended from the atmosphere or how much it impacted ozone levels on the West Coast. "People have been working on this for 15 years now, but we're raising it to the next level," said Owen Cooper, a researcher at NOAA's Earth System Research Laboratory and the Cooperative Institute for Research in Environmental Sciences, both in Boulder.

The study improved upon previous research in two important ways. First, scientists determined how the ozone dropped from the atmosphere to the Earth's surface. Second, they figured out how much of the surface ozone in the western United States could be attributed to pollution from China, Korea, Japan and the Southeast Asian countries.

A new, high-resolution model combined global emissions data from human and natural sources with chemistry that simulates the production of ozone. The scientists then verified this model against observations from ozone-measuring devices attached to balloons and aircraft. Satellites were also used to track the plumes, which travel two to five miles above the Pacific Ocean.

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"Not many studies have looked at how this pollution descends to the surface," said Meiyun Lin, a researcher with NOAA's Geophysical Fluid Dynamics Laboratory and the Cooperative Institute for Climate Science at Princeton University in New Jersey.

Lin said the descent is caused by a semi-permanent high-pressure system off the coast of California. When the plume collides with this system, the ozone is forced down toward the surface.

The air quality standard for surface ozone is 75 parts per billion -- a level set by the EPA.

On an average spring day, East Asia contributes ozone concentrations of four to eight parts per billion over the western United States. But when another plume reaches the west coast, which happens once every seven to 10 days, these numbers can spike to between eight and 15 parts per billion.

But these plumes usually account for less than 20 percent of the surface ozone in areas like California and Arizona. Fossil fuel emissions, wildfires, and lightning are among the other sources.

The researchers found that 20 percent of the days when surface ozone exceeded 60 parts per billion and 53 percent of the days when levels exceeded 75 parts per billion could be attributed to Asia's pollution plumes.

"The Asian contribution can push the already high levels over the limit," said Lin. "We should be concerned about it."

Asian pollution exerts the most influence during the springtime, Lin said, when winds are strong and the ozone has a longer lifetime. In the summer, by contrast, storms remove ozone from the atmosphere through precipitation.

Impacts from the Asian pollution plumes can reach as far into the continental United States as the Rocky Mountains, and they tend to have the greatest impact in areas of high elevation.

People and plants alike experience negative effects from exposure to high ozone concentrations. Respiratory issues are the most common problem for people, particularly the young, aging or asthmatic.

Plants absorb ozone through the pores on their leaves, which can be detrimental to their productivity. This is of particular concern in the highly productive agricultural regions of California. Cooper said the adverse effects of ozone on U.S. crop production could be significant.

Based on their findings in this study, Cooper and Lin said the next step is to look at the long-term implications. Asian emissions have been on the rise for the past 30 years, and as the continent continues to develop, Lin anticipates that the emissions will increase over the next decade.

"When an Asian country grows, certainly it emits more pollution," Lin said. "But on the other side, the U.S. emissions are expected to decrease."

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